The IS-95 Code Division Multiple Access (CDMA) system, also known as CDMAOne, is a digital cellular technology that was the first standard to use CDMA for commercial mobile communications. The IS-95 CDMA system introduced several key features that contributed to its success and paved the way for subsequent CDMA standards. Here are four significant features of the IS-95 CDMA system:
1. Spread Spectrum Technology:
- The IS-95 CDMA system is based on spread spectrum technology, a form of digital modulation that spreads the signal over a wide frequency band using a unique code for each user.
- Spread spectrum allows multiple users to share the same frequency band simultaneously without mutual interference. Each user is assigned a unique spreading code, and the signals from different users can coexist in the same spectrum.
2. Soft Handoff:
- IS-95 introduced the concept of “soft handoff,” which allows a mobile device to be in communication with multiple base stations simultaneously during a handover.
- Soft handoff improves call quality and system reliability by reducing the likelihood of call drops during transitions between cells. The mobile device can seamlessly switch between different base stations, enhancing the continuity of communication.
3. Power Control:
- The IS-95 CDMA system employs power control mechanisms to adjust the transmit power of mobile devices. Power control is crucial for optimizing system capacity and mitigating interference.
- By dynamically adjusting the transmit power based on the quality of the communication link, power control ensures that each user’s signal reaches the base station with the required strength, improving overall network efficiency.
4. Forward and Reverse Channels:
- The IS-95 CDMA system operates using forward and reverse channels for communication between the mobile device and the base station.
- The forward channel carries information from the base station to the mobile device, including voice and data, while the reverse channel transmits signals from the mobile device to the base station.
- Both channels use CDMA to enable multiple access and efficient communication between multiple users in both directions.
These features collectively contribute to the efficiency, reliability, and capacity of the IS-95 CDMA system. Spread spectrum technology forms the foundation for multiple access, soft handoff enhances call continuity, power control optimizes network resources, and the use of forward and reverse channels enables bidirectional communication. The success of the IS-95 CDMA system laid the groundwork for subsequent CDMA-based standards, including CDMA2000 and 3GPP2 standards.